User Guide
GNU Image Manipulation Program
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Bezier curve
A spline is a curve which is defined mathematically and has a set of control points. A Bezier spline is a cubic spline which
has four control points, where the first and last control points (knots or anchors) are the endpoints of the curve and the
inner two control points (handles) determine the direction of the curve at the endpoints.
In the non-mathematical sense, a spline is a flexible strip of wood or metal used for drawing curves. Using this type of
spline for drawing curves dates back to shipbuilding, where weights were hung on splines to bend them. The outer control
points of a Bezier spline are similar to the places where the splines are fastened down and the inner control points are
where weights are attached to modify the curve.
Bezier splines are only one way of mathematically representing curves. They were developed in the 1960s by Pierre Bezier,
who worked for Renault.
Bezier curves are used in GIMP as component parts of Paths.
The image above shows a Bezier curve. Points P0 and P3 are points on the Path, which are created by clicking with the
mouse. Points P1 and P2 are handles, which are automatically created by GIMP when you click on the line between P0
and P3 and stretch it. They change position when you stretch the curve in different ways.
The image above shows a path which consists of two components, having both straight and curved segments, being worked
on with the Path tool. Here, the open circle indicates the selected anchor and the two open squares are the two handles
which are associated with this anchor from the curves on either side of it.
Bitmap
From The Free On-line Dictionary of Computing (13 Mar 01) :
bitmap — A data file or structure which corresponds bit for bit with an image displayed on a screen, probably in
the same format as it would be stored in the display’s video memory or maybe as a device independent bitmap.
A bitmap is characterised by the width and height of the image in pixels and the number of bits per pixel which
determines the number of shades of grey or colours it can represent. A bitmap representing a coloured image
(a ‘pixmap’ ) will usually have pixels with between one and eight bits for each of the red, green, and blue
components, though other colour encodings are also used. The green component sometimes has more bits than
the other two to cater for the human eye’s greater discrimination in this component.
BMP
BMP is an uncompressed image file format designed by Microsoft and mainly used in Windows. Colors are typically
represented in 1, 4 or 8 bits, although the format also supports more. Because it is not compressed and the files are large,
it is not very well suited for use in the internet.
Bump mapping
Bump mapping is a technique for displaying extremely detailed objects without increasing the geometrical complexity of
the objects. It is especially used in 3-dimensional visualization programs. The trick is to put all the necessary information
into a texture, with which shadowing is shown on the surface of the object.
Bump mapping is only one (very effective) way of simulating surface irregularities which are not actually contained in the
geometry of the model.